A retinaculum (plural retinacula) is a band of thickened deep fascia around tendons that holds them in place. It is not part of any muscle. Its function is mostly to stabilize a tendon. The term retinaculum is New Latin, derived from the Latin verb retinere (to retain). Specific retinacula include: A retinaculum (plural retinacula) is a band of thickened deep fascia around tendons that holds them in place. It is not part of any muscle. Its function is mostly to stabilize a tendon. The term retinaculum is New Latin, derived from the Latin verb retinere (to retain). Specific retinacula include: